1. Rabbitt, J. C., Amer. Min., 33, 263 (1948).
2. Deer, W. A., Howie, R. A., and Zussman, J., Rock-Forming Minerals, 2, 216, 236, 212 (Longmans, London, 1963).
3. Mueller, R. F., Amer. J. Sci., 258, 449 (1960).
4. Warren, B. E., and Modell, D. I., Z. Krist., 75, 161 (1930).
5. Ghose, S., Acta Cryst., 14, 622 (1961).